Method for producing n-alkenyl amides

ABSTRACT

A process for preparing N-alkenyl-amides by reacting the corresponding NH-amides with acetylenes in the liquid phase in the presence of basic alkali metal compounds and of a cocatalyst comprises using as the cocatalyst compounds of the general formulae (Ia) and/or (Ib)  
     R 1 O—(CH 2 CH 2 CH 2 CH 2 O) n —H  (Ia):  
     R 1 O—(CH 2 CH 2 CH 2 CH 2 O) n —R 2 ,  (Ib):  
     where n is 1, 2 or 3 and R 1  and R 2  are independently C 1 - to C 6 -alkyl or C 2 - to C 6 -alkenyl, or together a butenyl unit.

[0001] The present invention leads to an improved process for preparingN-alkenyl-amides by reacting the corresponding NH-amides with acetylenesin the liquid phase in the presence of basic alkali metal compounds anda cocatalyst.

[0002] N-Alkenyl-amides are used as monomers in the manufacture ofplastics and paints. Polyvinylamides are used for example as laundrydetergent assistants, as auxiliaries in cosmetic and medical productsand also for stabilizing and clarifying beers and fruit juices.Polyvinyl-lactams, especially polyvinylpyrrolidone polymers, are widelyused, for example as dispersants for pigments, as laundry detergentassistants, as auxiliaries in cosmetic and medical products and also asauxiliaries in textile processing and adhesive technology.

[0003] N-Alkenyl-lactams are produced on an industrial scale by reactingthe corresponding NH-lactams with acetylenes in the presence of basiccatalysts (see W. Reppe et al., Justus Liebigs Ann. Chem., 601 (1956)page 135-8 and DE-Auslegeschrift 1 163 835).

[0004] DE-Offenlegungsschrift 3 215 093 discloses a process forvinylating 2-pyrrolidone with ethyne in the presence of basic catalystsand in the additional presence of a polyoxyalkylene compound ascocatalyst. Useful polyoxyalkylene compounds are said to be crown ethers(eg 18-crown-6), polyoxyethylene, polyoxypropylene, selectively cappedby alkyl or phenyl groups. Conversions up to 63% and selectivitiesaround 90% are reported, the corresponding yield being not more 57%. Theformation of polymeric residues is reduced. However, the cocatalystsmentioned are costly materials which are generally not recoverable,since they have high boiling points and therefore remain in thedistillation bottoms together with the polymeric byproducts. Inaddition, they are not stable in the strongly basic medium of thereaction.

[0005] U.S. Pat. No. 5,665,889 describes a method for the production ofN-vinyl-2-pyrrolidone from 2-pyrrolidone and ethyne in the presence ofbasic alkali metal compounds using cocatalysts comprising hydroxyend-capped ether oligomers, for example polytetrahydrofuran, or lineardiols having at least 4 carbon atoms, for example, 1,4-butanediol. Thevinylation takes place at a temperature ranging from 100 to 200° C., andat a pressure ranging from 7.5 to 30 atm (from 7.6 to 30 bar) in thecourse of a reaction time of several hours. The use of 1,4-butanediolproduced a yield of only 77.2% even after a reaction time of 4 hours.The present inventors have determined that these cocatalysts, which havehigh boiling points, are generally impossible to separate from thepolymeric byproducts or in the case of the use of 1,4-butanediol can beseparated from the product of value only by means of inconvenientdistillative or chemical methods.

[0006] It is an object of the present invention to develop a process forpreparing N-alkenyl-amides that does not have the recited.disadvantages, that permits yields of more than 80% and that makes thepure product obtainable in a simple manner.

[0007] We have found that this object is achieved by a process forpreparing N-alkenyl-amides by reacting the corresponding NH-amides withacetylenes in the liquid phase in the presence of basic alkali metalcompounds and of a cocatalyst, which comprises using as the cocatalystcompounds of the general formulae (Ia) and/or (Ib)

R¹O—(CH₂CH₂CH₂CH₂O)_(n)—H  (Ia):

R¹O—(CH₂CH₂CH₂CH₂O)_(n)—R²,  (Ib):

[0008] where n is 1, 2 or 3 and R¹ and R² are independently C₁- toC₆-alkyl or C₂- to C₆-alkenyl, or together a butenyl unit.

[0009] The process of the invention provides N-alkenyl-amides in highselectivity and high yield from the corresponding NH amides andacetylenes in the presence of basic alkali metal compounds and of aninexpensive cocatalyst which is simple to remove again from the reactionmixture.

[0010] An essential feature of the process according to the invention isthe presence of a cocatalyst (Ia) and/or (Ib)

R¹O—(CH₂CH₂CH₂CH₂O)_(n)—H  (Ia):

R¹O—(CH₂CH₂CH₂CH₂O)_(n)—R²,  (Ib):

[0011] where n is 1, 2 or 3

[0012] and R¹ and R² are independently branched or unbranched C₁- toC₆-alkyl, for example methyl, ethyl, propyl, 1-methylethyl, butyl,1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, pentyl,1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl,1-ethylpropyl, hexyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl,1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl,1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl,2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1-ethylbutyl,2-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl,1-ethyl-1-methylpropyl and 1-ethyl-2-methylpropyl,

[0013] or branched or unbranched C₂- to C₆-alkenyl having a double bondin any desired position, for example ethenyl (vinyl), 1-propenyl,2-propenyl, 1-methylethenyl, 1-butenyl, 2-butenyl, 3-butenyl,1-methyl-1-propenyl, 2-methyl-1-propenyl, 1-methyl-2-propenyl,2-methyl-2-propenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl,1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl and 5-hexenyl,

[0014] or R¹ and R² are together a butenyl unit, specificallyCH₂CH₂CH₂CH₂,

[0015] or mixtures thereof.

[0016] Examples of useful cocatalysts (Ia) and/or (Ib) for the processof the invention are 4-methoxy-1-butanol, 4-ethoxy-1-butanol,4-propoxy-1-butanol, 4-butoxy-1-butanol, 1,4-dimethoxybutane,1,4-diethoxybutane, 1,4-dipropoxybutane, 1,4-dibutoxybutane,1-ethoxy-4-methoxybutane, 1-propoxy-4-methoxybutane,1-butoxy-4-methoxybutane, 1-propoxy-4-ethoxybutane,1-butoxy-4-ethoxybutane, 1-butoxy-4-propoxybutane, 4-vinyloxy-1-butanol,4-(isopropenyloxy)-1-butanol, 4-propenyloxy-1-butanol,1,4-divinyloxybutane, 1,4-bis(isopropenyloxy)butane,1,4-bis(propenyloxy)butane, 1-vinyloxy-4-methoxybutane,1-vinyloxy-4-ethoxybutane, 1-vinyloxy-4-propoxybutane,1-(isopropenyloxy)-4-propoxybutane, 1-(propenyloxy)-4-propoxybutane,4-(4′-methoxy-1′-butoxy)-1-butanol, 4-(4′-ethoxy-1′-butoxy)-1-butanol,4-(4′-vinyloxy-1′-butoxy)-1-butanol, bis(4-methoxy-1-butyl) ether,bis(4-ethoxy-1-butyl) ether, bis(4-vinyloxy-1-butyl) ether, 10-crown-2,15-crown-3 and 20-crown-4.

[0017] Preference is given to using cocatalysts of the formulae (Ia)and/or (Ib) where R¹ and R² are independently ethyl or vinyl, forexample 4-ethoxy-1-butanol, 1,4-diethoxybutane, 4-vinyloxy-1-butanol,1,4-divinyloxybutane, 1-vinyloxy-4-ethoxybutane,4-(4′-ethoxy-1′-butoxy)-1-butanol, 4-(4′-vinyloxy-1′-butoxy)-1-butanol,bis(4-ethoxy-1-butyl) ether and bis(4-vinyloxy-1-butyl) ether ormixtures thereof.

[0018] Particular preference is given to using 4-ethoxy-1-butanol,1,4-diethoxybutane, 4-vinyloxy-1-butanol, 1,4-divinyloxybutane,1-vinyloxy-4-ethoxybutane or mixtures thereof. Very particularpreference is given to using 1,4-diethoxy-butane, 1,4-divinyloxy-butaneor mixtures thereof.

[0019] The cocatalysts to be used in the process of the invention areobtainable by the following syntheses:

[0020] (a) 4-Alkenyloxy-1-butanols and 1,4-dialkenyloxybutanes areformed by reacting 1,4-butanediol with acetylenes in the presence of abasic catalyst and separating the product by distillation. In this wayit is possible for example to obtain 4-vinyloxy-1-butanol and1,4-divinyloxybutane by reacting 1,4-butanediol with ethyne anddistillative workup.

[0021] (b) 4-Alkoxy-1-butanols and 1,4-dialkoxybutanes are prepared bycatalytic hydrogenation of the 4-alkenyloxy-1-butanols and1,4-dialkenyloxybutanes obtained according to (a). Suitablehydrogenation catalysts are known to one skilled in the art. It ispossible to use, for example, noble metal powders, mohr or black,supported hydrogenating metals, for example noble metals or copper oncharcoal or oxidic carrier materials. 1,4-Diethoxybutane can thus beobtained by hydrogenating 1,4-divinyloxybutane.

[0022]  Alternatively, the 4-alkoxy-1-butanols and 1,4-dialkoxybutanesare also obtainable by etherifying 1,4-butanediol with the correspondingalkanols according to etherification methods known to one skilled in theart.

[0023] (c) 1-Alkenyloxy-4-alkoxybutanes are obtained by reacting the4-alkoxy-1-butanols obtained according to (b) with acetylenes accordingto (a).

[0024] (d) Alkoxy and alkenyloxy derivatives of dibutylene glycol andtributylene glycol are obtainable by intermolecular etherification of1,4-butanediol and subsequent derivatization corresponding to (a) to(c).

[0025] (e) 1,4-Butanediol crown ethers are obtainable by intermolecularetherification of 1,4-butanediol.

[0026] The cocatalysts to be used in the process of the invention areeasy to remove from the reaction mixture, especially from theN-alkenyl-amide products of value, compared with prior art cocatalysts.The greater the gap between the boiling points of the cocatalysts andthose of the N-alkenyl-amides, whether in the direction of lower orhigher boiling points, the simpler it is to remove the N-alkenyl-amidesprepared. Generally the 1,4-dialkenyloxybutanes and 1,4-dialkoxybutaneshave a distinctly lower boiling point than the N-alkenyl-amide productsof value, so that the cocatalysts are removed by distillation before theproducts of value. In the case of the alkoxy and alkenyloxy derivativesof dibutylene glycol and of tributylene glycol and also the1,4-butanediol crown ethers, by contrast, the boiling points of theN-alkenyl-amide products of value are generally lower, so that thehigher molecular weight cocatalysts are removed by distillation afterthe products of value.

[0027] NH-amides useful as starting materials in the process of theinvention include cyclic and noncyclic amides which contain the“—CO—NH—” unit in their charge-neutral form.

[0028] Useful noncyclic amides include for example the N-alkyl-amides ofbranched and unbranched, saturated and unsaturated C₁- to C₂₂-carboxylicacids, having branched and unbranched, saturated and unsaturated C₁- toC₁₀-alkyl groups on the amide nitrogen. Examples of noncyclic NH-amidesare the methyl-, ethyl-, propyl-, 1-methylethyl-, butyl-,1-methylpropyl-, 1,1-dimethylethyl-, pentyl-, hexyl, heptyl-, octyl-,nonyl- or decyl-amides of formic acid, acetic acid, propionic acid,butyric acid, valeric acid, isovaleric acid, pivalic acid, caproic acid,2-ethylbutyric acid, enanthic acid, caprylic acid, 2-ethylhexanic acid,pelargonic acid, isononanoic acid, capric acid, neodecanoic acid, lauricacid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleicacid, linolenic acid, arachidic acid and behenic acid. Preferrednoncyclic NH-amides are N-methyl-acetamide, N-methyl-propionamide andN-ethyl-acetamide.

[0029] Particular preference is given to the use of cyclic NH-amides,which are known as NH-lactams. Useful NH-lactams for the process of theinvention include 4- to 12-membered NH-lactams, for example2-pyrrolidone, 2-piperidone, ε-caprolactam and alkyl derivativesthereof, for example 3-methyl-2-pyrrolidone, 4-methyl-2-pyrrolidone,5-methyl-2-pyrrolidone, 3-ethyl-2-pyrrolidone, 3-propyl-2-pyrrolidone,3-butyl-2-pyrrolidone, 3,3-dimethyl-2-pyrrolidone,3,5-dimethyl-2-pyrrolidone, 5,5-dimethyl-2-pyrrolidone,3,3,5-trimethyl-2-pyrrolidone, 5-methyl-5-ethyl-2-pyrrolidone,3,4,5-trimethyl-2-pyrrolidone, 3-methyl-2-piperidone,4-methyl-2-piperidone, 5-methyl-2-piperidone, 6-methyl-2-piperidone,6-ethyl-2-piperidone, 3,5-dimethyl-2-piperidone,4,4-dimethyl-2-piperidone, 3-methyl-ε-caprolactam,4-methyl-ε-caprolactam, 5-methyl-ε-caprolactam, 6-methyl-ε-caprolactam,7-methyl-ε-caprolactam, 3-ethyl-ε-caprolactam, 3-propyl-ε-caprolactam,3-butyl-ε-caprolactam, 3,3-dimethyl-ε-caprolactam or7,7-dimethyl-ε-caprolactam. Preference is given to using theunsubstituted 4- to 12-membered H-lactams

[0030] here p is from 2 to 10, for example β-propiolactam, 2-pyrrolidone(γ-butyrolactam), 2-piperidone (δ-valerolactam), ε-caprolactam and alsoalkyl-substituted derivatives thereof. Particular preference is given tothe use of 2-pyrrolidone (γ-butyrolactam), 2-piperidone (δ-valerolactam)and ε-caprolactam.

[0031] Acetylenes used in the process of the invention are preferablyunbranched and branched alkynes having 2 to 6 carbon atoms and aterminal triple bond, for example ethyne, propyne, 1-butyne, 1-pentyne,1-hexyne. Particular preference is given to the use of ethyne andpropyne, especially ethyne.

[0032] The cocatalyst to be used according to the invention isadvantageously used in an amount of from 0.1 to 10% by weight, based onthe NH-amide used. An amount of from 0.5 to 5% by weight is particularlypreferred.

[0033] Basic alkali metal compounds useful as catalyst in the process ofthe invention include the oxides, hydroxides and/or alkoxides oflithium, sodium, potassium, rubidium and/or cesium and also mixturesthereof. Preferred alkoxides are compounds of low molecular weightalcohols, for example methoxide, ethoxide, propoxide, 1-methyl-ethoxide,butoxide, 1-methyl-propoxide, 2-methyl-propoxide and1,1-dimethyl-ethoxide. Preference is given to using the oxides,hydroxides and/or alkoxides of sodium and/or potassium. Particularpreference is given to sodium hydroxide and potassium hydroxide. Thebasic alkali metal compounds may be used as solids or solutions in wateror alcohol. Preference is given to the use of solid, water- andalcohol-free alkali metal compounds. Mixtures of various alkali metalcompounds are also possible.

[0034] The reaction with the acetylene may be carried out at a molarratio of from 0.02 to 6.0%, preferably from 0.05 to 4.0%, between thetotal of basic alkali metal compounds used and the NH-amide.

[0035] The process of the invention may be carried out as follows:

[0036] The first step of the process according to the invention may beto dissolve the cocatalyst in the NH-amide. However, the addition mayalso take place later.

[0037] The next step is to contact the basic alkali metal compounds withthe NH-amide. It may be pointed out that the NH-amide may at this pointalready include the requisite amount of cocatalyst. The alkali metalcompound is added, for example, by dissolving it in the liquid NH-amideor by adding a solution of the alkali metal compounds to the NH-amide.It is also possible to dilute the NH-amide, or the solution of thealkali metal compound in the NH-amide, with a suitable solvent, forexample in order to influence the reaction characteristics. Usefulsolvents dissolve both the NH-amide and the basic catalyst relativelyreadily and do not react chemically with the compounds used, ie have inparticular no acidic centers which would scavenge the basic groups, andthey are relatively easy to remove again, preferably by distillation,from the system after the synthesis of the N-alkenyl-amides. Examples ofuseful solvents are N-methylpyrrolidone, tetrahydrofuran or dialkylethers of glycols, di-, oligo- or polyglycols.

[0038] The solution of the basic alkali metal compounds in the NH-amideor its solutions is generally prepared according to customary methods bycontacing the catalyst solid with the liquid by thorough mixing. Thisprovides an accelerated dissolution of the solid and counteracts anylocal heating due to the heat of dissolution. Suitable apparatuses areknown to those skilled in the art. Stirred tanks may be mentioned by wayof example without limitation. The liquid is charged initially and thecatalyst solid is added, if appropriate over a period of time,continuously or a little at a time with thorough mixing. When solutionsof the basic alkali metal compounds in water or alcohols are used, theprocedure is basically similar. Here too those skilled in the art wouldknow of suitable methods. It is also possible to add the cocatalysttogether with the alkali metal compound.

[0039] The solution of the basic alkali metal compounds in the NH-amidemay be prepared not only in highly concentrated form ascatalyst/NH-amide stock solution but also in low-concentrated form ascatalyst/NH-amide reaction solution. The highly concentratedcatalyst/NH-amide stock solution is set to a high catalystconcentration, which may be as high as the solubility limit, while thelow-concentrated catalyst/NH-amide reaction solution is set to thecatalyst concentration required for the reaction with acetylene. It willbe appreciated that all stages in between are possible as well.

[0040] The reaction of the NH-amides with the alkali metal compoundsbyproduces water or alcohols in an equilibrium reaction in liquid form.Water or the alcohols formed remain in solution and, owing to theequilibrium relation, prevent complete conversion between the NH-amideand the basic alkali metal compounds. Specific removal of the waterand/or alcohol of reaction formed results in a shift of the equilibriumin the direction of the alkali metal salt of the NH-amide, so that thesalt mentioned may be obtained in sufficient concentration. The additionof the basic alkali metal compounds to the NH-amide may take place notonly in a separate process step but also during the removal of thewater/alcohol of reaction. In addition, the cocatalyst may be added in aseparate step after addition of the alkali metal compound or before orduring the removal of the water/alcohol of reaction.

[0041] The advantageous removal of the water and/or alcohol of reactionformed contributes to obtaining a particularly high selectivity to andyield of N-alkenyl-amides.

[0042] Particularly preferred methods for removing the water or lowmolecular weight alcohols of reaction are evaporation, binding to asuitable drier (adsorption) and removal through a suitable membrane. Themethods mentioned may even be employed when aqueous or alcoholiccatalyst solutions are used.

[0043] Evaporation exploits the large difference in vapor pressurebetween water/low molecular weight alcohol and the NH-amide. The wateror alcohol of reaction is preferably evaporated at elevated temperaturebetween 50 and 150° C. and a reduced pressure between 0.1 kPa (1 mbarabs) and a subatmospheric pressure. Evaporation may be effected invarious ways. For example, it may be effected in a mixed vessel (egstirred tank) by heating and/or applying a reduced pressure. Similarly,stripping with an inert gas, for example nitrogen, is possible.Evaporation may also be effected by passing the solution through anevaporator. Such equipment is described in the pertinent technicalliterature (see for example Ullmann's Encyclopedia of IndustrialChemistry, 6^(th) edition, 1998 Electronic Release, Chapter“Evaporation”). A particularly preferred method of evaporation isdistillation. It may be carried out discontinuously, semicontinuously orcontinuously. In a discontinuous distillation, the NH-amide, thecatalyst, which may be completely or else only partially dissolved, and,if appropriate, the cocatalyst are initially charged to the distillationflask and the temperature is raised and/or the pressure reduced todistill off the water or alcohol of reaction. In a semicontinuousdistillation, for example, a solution of the catalyst in the NH-amide,which includes the cocatalyst, if appropriate, is fed to the column partand the water or alcohol of reaction is distilled off continuously. Thewater- or alcohol-free product collects in the distillation flask. Acontinuous distillation differs from a semicontinuous distillationmainly in that the water- or alcohol-free product is continuouslyremoved from the bottom region. The distillations are preferably carriedout at a pressure less than 0.1 MPa (1 bar abs).

[0044] The use of a drier exploits the exothermic adsorption of smallmolecules on suitable solids having large surface areas. A particularlyimportant application is the removal of water. The technical literaturedescribes a multiplicity of suitable driers (see for example Ullmann'sEncyclopedia of Industrial Chemistry, 6^(th) edition, 1998 ElectronicRelease, Chapter “Zeolites”). Useful driers include for example, withoutlimitation, zeolitic molecular sieves, for example the type 13X. Thedrying may also be effected in various ways. In one variant, forexample, the drier is disposed directly in the reaction system in whichthe later reaction with the acetylene takes place. In another variant,the solution is passed through a bed of the drier and only subsequentlyintroduced into the alkenylation reactor.

[0045] The third option mentioned, removal via a membrane, exploits thesize difference between water or the low molecular weight alcohols andthe teriary dialcohols. In one embodiment, the membrane is disposeddirectly in the reaction system in which the later reaction with theacetylene takes place. In another embodiment, the solution is passedover a membrane in an upstream apparatus. Suitable membranes aredescribed in the pertinent technical literature (see for exampleUllmann's Encyclopedia of Industrial Chemistry, 6^(th) edition, 1998Electronic Release, Chapter “Membranes and Membrane SeparationProcesses”).

[0046] The water and/or alcohol of reaction is preferably removed by theabove-discussed methods of evaporation, adsorption and/or by a membrane.Any desired combinations between the individual methods are possible aswell and may even be advantageous. Without limitation there may bementioned a two-stage distillation, a distillation with downstreamadsorption or a removal by means of a membrane with downstreamadsorption. Particular preference is given to using distillativeremoval, which is most preferably carried out in a single stage, at apressure of less than 0.1 MPa (1 bar abs).

[0047] The water or alcohol of reaction is advantageously removed to aresidual level of less than 1% by weight, preferably less than 0.5% byweight, particularly preferably less than 0.2% by weight, based on thetotal amount of liquid.

[0048] The cocatalyst may also be added according to the invention afterthe removal of the water or alcohol of reaction. Care must be taken toensure here that the cocatalyst feed is free of water and low molecularweight monoalcohols, for example methanol, ethanol or propanol, in orderthat the effect of the preceding stage is not diminished.

[0049] When the cocatalyst contains water or low molecular weightmonoalcohols, these are to be removed before the cocatalyst is added.But in this case it is preferable to add the cocatalyst to theNH-amide/catalyst solution upstream of the process stage for removingthe water or alcohol of reaction.

[0050] The reaction with the acetylene is effected by contacting theabove-described, NH-amide-, catalyst- and cocatalyst-containing,beneficiated (ie water- and monoalcohol-free) solution with theacetylene in the liquid phase. The NH-amide/catalyst/cocatalyst solutionmay also have been diluted with a water- and monoalcohol-free solvent.Useful solvents generally include all solvents which are also useful inthe solution of the NH-amide and of the basic catalysts. Examples ofuseful solvents are N-methylpyrrolidone, tetrahydrofuran or dialkylethers of glycols, di-, oligo- or polyglycols. The reaction ispreferably carried out in undiluted form, ie without addition of afurther solvent.

[0051] If a catalyst/NH-amide solution was prepared with a catalystconcentration above the level required for the reaction with acetylene,for example a catalyst/NH-amide stock solution, and treated according tothe invention, it must now be diluted with further, water- andalcohol-free NH-amide. The diluting may take place both outside andinside the alkenylation reactor. The low-concentrated catalyst/NH-amidereaction solution treated according to the invention can be useddirectly.

[0052] The reaction with acetylene can be carried out in various ways.In the semicontinuous process, the entire NH-amide/catalyst/cocatalystsolution is initially charged and the acetylene metered in at the rateof reaction. The product solution is normally not removed until afterthe reaction has ended. In the continuous process, theNH-amide/catalyst/cocatalyst solution and the acetylene are introducedcontinuously and the corresponding product solution is removedcontinuously.

[0053] The alkenylation is generally carried out at from 100 to 200° C.,preferably from 130 to 180° C., particularly preferably from 140 to 160°C. It is generally carried out at an acetylene pressure of less than 5MPa (50 bar abs), preferably less than 3 MPa (30 bar abs), mostpreferably less than 2.4 MPa (24 bar abs). However, the total pressureof the system may be significantly higher, since the gas atmosphereabove may for example additionally include inert gases, such as nitrogenor noble gases, which may be introduced by specific injection. So thetotal pressure in the system may easily be 20 MPa (200 bar abs) forexample. If relatively high molecular weight acetylenes are used, thenthe autogenous acetylene presure will be very low and may for example bedistinctly below 0.1 MPa (1 bar abs). Low molecular acetylenes, forexample ethyne, propyne and 1-butyne, are generally set to an acetylenepressure of greater than 0.1 MPa (1 bar abs). This provides aneconomical space-time yield. An alkenylation with ethyne as theacetylene is preferably carried out at an acetylene (ethyne) pressure offrom 0.5 to 3.0 MPa (5 to 30 bar abs), particularly preferably from 0.8to 2.4 MPa (8 to 24 bar abs), most preferably from 1.6 to 2.0 MPa (16 to20 bar abs).

[0054] The reactor used for the alkenylation may in principle be anyapparatus described for gas-liquid reactions in the pertinent technicalliterature. A high space-time yield requires thorough mixing between theNH-amide/catalyst/cocatalyst solution and the acetylene. Nonlimitingexamples are stirred tanks, stirred tank batteries, flow tubes(preferably with internal fitments), bubble columns and loop reactors.The reactor effluent is worked up according to known methods. Preferenceis given to a distillation into a plurality of fractions. Distillationsare preferably carried out at a pressure less than 0.1 MPa (1 bar abs).It is particularly preferable to recover not only the N-alkenyl-amidebut also the cocatalysts as a fraction. Depending on the choice ofcocatalysts to be used according to the invention, they are separatedoff in a lower boiling or higher boiling fraction before or after theN-alkenyl-amide. Various fractions may be mentioned without limitation:cocatalyst (before or after N-alkenyl-amide), N-alkenyl-amide,unconverted NH-amide, various intermediate boilers, low boilers and highboilers. According to intention, these may be recovered as crudefraction or in high purity. It is also possible to combine somefractions. The distillation may be carried out continuously,semicontinuously or discontinuously. In addition, it may be carried outin one column, with or without sidestream takeoffs, as well as in aplurality of consecutive columns. Suitable methods will be known tothose skilled in the art. The process of the invention, as described, isa simple way of obtaining N-alkenyl-amide in a purity of above 99.8%.

[0055] The optionally removed unconverted NH-amide may be recycled inthe process of the invention without further purification measures. Forthis, it is not necessary to recover the starting material in highpurity, so that a crude-distilled fraction may be used as well. However,it is advantageous to remove those products having a distinctly higherboiling point.

[0056] The process of the invention allows, usually advantageously, theremoved cocatalysts to be recycled. It is not necessary to recover themin high purity, so that a crude-distilled fraction may be used as well.However, it is advantageous to remove those products having a distinctlyhigher boiling point. Any losses of cocatalysts are to be made good byaddition of virgin cocatalysts.

[0057] The process of the invention is particularly preferable forpreparing

[0058] N-vinyl-2-pyrrolidone N-vinyl-2-piperidone(N-Vinyl-γ-butyrolactam) (N-Vinyl-δ-valerolactam)

[0059] N-vinyl-ε-caprolactam

[0060] and mixtures thereof. Starting materials for this are thecorresponding NH-lactams 2-pyrrolidone (γ-butyrolactam), 2-piperidone(δ-valerolactam) and ε-caprolactam. The preparation ofN-vinyl-ε-caprolactam is very particularly preferred.

[0061] In a general embodiment, the basic alkali metal compound(catalyst) and the cocatalyst are added a little at a time into theliquid, optionally solvent-diluted, NH-amide and mixed in. The resultingsolution is then passed over a zeolitic drier into a stirred tank. Thepresence of the drier removes the water of reaction. The then almostanhydrous solution has the acetylene passed into it with thorough mixingat from 100 to 200° C. The preferred ethyne is preferably introduced upto a pressure of 2.4 MPa (24 bar abs). Consumed acetylene isreplenished. After the absorption of acetylene has ceased, the reactionsystem is depressurized. The reaction solution is transferred into adistillation column and the N-alkenyl-amide is isolated overhead in highpurity after removal of the lower boiling components.

[0062] In a further general embodiment, a mixing vessel is used toprepare an almost concentrated solution (ie about 80% of maximumsolubility) of the basic alkali metal compound in the NH-amide. Thissolution is continuously fed to a vacuum distillation column and thewater of reaction formed is taken off overhead. The water-freecatalyst/NH-amide solution is continuously removed from the bottomregion and admixed with further anhydrous NH-amide and with anhydrouscocatalyst. The recycling streams are also fed in at this point. Thereactant mixture is then fed into a continuous loop reactor where thereaction with the acetylene is carried out at from 100 to 200° C. Thepreferred ethyne is preferably introduced up to a pressure of 2.4 MPa(24 bar abs). The reaction solution is continuously removed from theloop reactor and worked up by distillation. The N-alkenyl-amide isisolated as pure product. Recovered uncoverted NH-amide and removedalkenylated cocatalyst are recycled.

[0063] In a third, particularly preferred embodiment, a mixing vessel isused to prepare a solution of about 2% by weight of potassium hydroxidein ε-caprolactam and admixed with about 1.0% by weight of1,4-diethoxybutane and/or 1,4-divinyloxybutane. This solution iscontinuously fed to a vacuum distillation column and the water ofreaction formed is taken off overhead. The almost anhydrous solution iscontinuously removed from the bottom region into a stirred tank wherethe semicontinuous reaction takes place with the gaseous ethyne at from140 to 160° C. and from 1.5 to 2.0 MPa (15 bis 20 bar abs). After thereaction has ended, the reactor contents are removed from the reactorinto a distillative workup stage where they are separated into lowboilers, comprising 1,4-diethoxybutane and/or 1,4-divinyloxybutane,N-vinyl-ε-caprolactam and high boilers. The N-vinyl-ε-caprolactam isrecovered in high purity.

[0064] The process of the invention provides a simple way of obtainingN-alkenyl-amides in very high yield and purity by reacting thecorresponding NH-amides with acetylenes in the presence of basic alkalimetal compounds and of a cocatalyst. The outstanding advantages over theprior art are in particular:

[0065] The use of a cocatalyst which is, in the case of the particularlypreferred 1,4-diethoxybutane or 1,4-divinyloxybutane, very inexpensive.

[0066] The ease of removal of the N-alkenyl-lactam from the reactionsolution and the very high purity attainable thereby.

[0067] The possibility to recover and reuse the cocatalyst.

EXAMPLES

[0068] Definitions

[0069] The conversion, selectivity and yield reported in the descriptionand the examples are defined by the following equations:

Conversion=[m _(before)(NH-amide)−m_(after)(NH-amide)]/mbefore(NH-amide)

Selectivity=m _(after)(N-alkenyl-amide)/[m _(before)(NH-amide)−m_(after)(NH-amide)]

Yield=Conversion×selectivity=/m _(after)(N-alkenyl-amide)/m_(before)(NH-amide)

[0070] where: m_(before)(NH-amide) is the mass of NH-amide usedm_(after)(NH-amide) is the unconverted mass of NH-amidem_(after)(N-alkenyl-amide) is the mass of N-alkenyl-amide formed, afterpurifying distillation.

[0071] Procedure

[0072] 100 g of ε-caprolactam were admixed with 2.5 g of KOH in eachcase and dissolved with stirring. Then the water of reaction was removedat 0.1 kPa (1 mbar abs) and 100° C. The almost anhydrous reaction batchwas then optionally admixed with cocatalyst, introduced into anautoclave and pressurized with nitrogen to 0.2 MPa (2 bar abs) at roomtemperature. After heating to 90° C., ethyne was injected to 1.2 MPa (12bar abs). Ethyne consumed by the reaction was replenished by continuousinjection to 1.2 MPa (12 bar abs). After 12 hours the run wasdiscontinued and the reaction product distilled. Analysis was by gaschromatography.

Example 1 Comparative Example Without Cocatalyst

[0073] Example 1 was carried out without addition of a cocatalyst. Theamount of ethyne taken up was 0.69 mol per mole of ε-caprolactam. Thedistillative workup yielded N-vinyl-ε-caprolactam in a yield of 77.9%. Aviscid distillation residue was obtained.

Example 2 Inventive

[0074] Example 2 was carried out by adding 1% by weight of1,4-diethoxybutane as cocatalyst. The amount of ethyne taken up was 0.87mol per mole of ε-caprolactam. The distillative workup yieldedN-vinyl-ε-caprolactam in a yield of 81.9%. A liquid distillation residuewas obtained.

Example 3 Inventive

[0075] Example 3 was carried out by adding 1% by weight of1,4-divinyloxybutane as cocatalyst. The amount of ethyne taken up was0.97 mol per mole of ε-caprolactam. The distillative workup yieldedN-vinyl-ε-caprolactam in a yield of 85.0%. A liquid distillation residuewas obtained.

[0076] A summary of the examples is reported in Table 1. The lowestyield of 77.9% was obtained without cocatalyst, under otherwiseidentical conditions. The two examples with cocatalyst gave a distinctlyhigher yield between 81.9 and 85.0%. The positive effect of thecocatalysts resulted in the formation of fewer byproducts, whichmanifested itself in the consistency of the distillation residue. TABLE1 Relative takeup of ethyne Conversion Selectivity Yield DistillationConsistency No. Cocatalyst [mol/mole] [%] [%] [%] residue of residue 1without 0.69 86.1 90.5 77.9 8.2 viscid (comparative example) 2 1% byweight of 0.87 93.7 87.4 81.9 11.8 liquid 1,4-diethoxybutane 3 1% byweight of 0.97 96.3 88.3 85.0 11.3 liquid 1,4-divinyloxybutane

We claim:
 1. A process for preparing N-alkenyl-amides by reacting thecorresponding NH-amides with acetylenes in the liquid phase in thepresence of basic alkali metal compounds and of a cocatalyst, whichcomprises using as the cocatalyst compounds of the general formulae (Ia)and/or (Ib) R¹O—(CH₂CH₂CH₂CH₂O)_(n)—H  (Ia):R¹O—(CH₂CH₂CH₂CH₂O)_(n)—R²,  (Ib): where n is 1, 2 or 3 and R¹ and R²are independently C₁- to C₆-alkyl or C₂- to C₆-alkenyl, or together abutenyl unit.
 2. A process as claimed in claim 1, wherein the cocatalystused comprises compounds of the formulae (Ia) and/or (Ib) where R¹ andR² are independently ethyl or vinyl.
 3. A process as claimed in claims 1to 2, wherein the cocatalyst used is 1,4-diethoxybutane or1,4-divinyloxybutane.
 4. A process as claimed in any of claims 1 to 3,wherein said cocatalyst (Ia) and/or (Ib) is used in an amount of from0.1 to 10% by weight, based on the NH-amide used.
 5. A process asclaimed in any of claims 1 to 4, wherein the basic alkali metalcompounds used are sodium hydroxide and/or potassium hydroxide.
 6. Aprocess as claimed in any of claims 1 to 5, wherein the basic alkalimetal compounds are used in a molar amount of from 0.05 to 4.0% of themolar amount of the NH-amide used.
 7. A process as claimed in any ofclaims 1 to 6, wherein the water and/or alcohol of reaction formed inthe course of the reaction between the basic alkali metal compounds andthe NH-amide is removed from the system by evaporation, by adsorptionand/or by a membrane.
 8. A process as claimed in any of claims 1 to 7,wherein the water and/or alcohol of reaction formed is removed from thesystem by distillation.
 9. A process as claimed in any of claims 1 to 8,wherein the reaction between the NH-amides and the acetylenes is carriedout at from 100 to 200° C. and at an acetylene pressure of less than 5MPa.
 10. A process as claimed in any of claims 1 to 9, wherein thecocatalyst is recovered and reused as cocatalyst.
 11. A process asclaimed in any of claims 1 to 10, wherein the N-alkenyl-amides preparedare N-alkenyl-lactams.
 12. A process as claimed in claim 11, wherein theN-alkenyl-lactams prepared are N-vinyl-2-pyrrolidone,N-vinyl-2-piperidone and/or N-vinyl-ε-caprolactam.